Is it acceptable to pigtail a copper wire to an aluminum 2 AWG SE cable? I came across a 100 AMP panel yesterday that was recently replaced and looked OK, with the exception of the this copper splice (pigtail) inside the panel. One side of the SE cable was aluminum and the other was pigtailed with a 12 inch section of copper.
A connection like that should have all of the items listed, but you should not be able to see them. The mechanical portion should be a split bolt, or an approved set screw connector. Then it is usually wrapped with a rubber insulating tape and then vinyl tape for protection. I have never seen a wire nut that was large enough for the connection you describe.